Many laser based devices such as laser printers and optical memories can be improved by incorporating arrays of independently controlled lasing elements. For example, a laser printer using an array of lasing elements can have higher printing speeds and better spot acuity than a printer using only a single lasing element.
Monolithic laser arrays usually output light at one wavelength. Typically, that wavelength is only variable over a small range. However, in many applications, including color printing, it is desirable to output multiple wavelengths that span a wide range; for example, from the infrared through the visible. In color printing this enables one to match laser characteristics to photoreceptor response windows, or to separate overlapping laser beams after scanning by using dichroic filters. When using an array of lasing elements to output multiple wavelengths it is almost always desirable to have low electrical, optical, and thermal crosstalk between the lasing elements.
As compared to present day monolithic laser arrays, nonmonolithic laser arrays can provide a greater range of laser beam characteristics (such as wavelength, polarization and spot sizes) and lower crosstalk. A nonmonolithic laser array usually consists of a plurality of individual laser diodes mounted on a support. In applications such as laser printing, the output laser beams must be accurately spatially separated. Thus, the lasing elements of the nonmonolithic array must be supported such that accurate positioning of the lasing elements is achieved.
Prior art nonmonolithic semiconductor laser arrays usually arrange their lasing elements along a planar support. Alignment of the lasing elements involves external manipulations of the lasing elements on the support. Such laser arrays suffer from several problems. A first is the difficulty of accurately aligning the laser outputs. A second is that achieving closely spaced laser elements is difficult since edge effects limit the minimum spacing between lasing elements, especially in arrays containing more than two elements.
An alternate approach is to vertically stack the lasing elements. Such an arrangement is used in U.S. Pat. No. 4,716,568, issued Dec. 29, 1987, to make an assembly of monolithic bars of diode laser emitters. In that assembly, the laser emitters in each bar are electrically connected in parallel, while the laser bars are electrically connected in series. Thus current simultaneously passes through all of the laser emitters, thereby precluding the separate addressing of the individual emitters.
Thus, there exists a need for methods and devices that enable close, accurate spacing of lasing elements in a nonmonolithic laser array without excessive thermal, optical, and/or electrical crosstalk. Such methods and devices are even more desirable if they permit the accurate orientation of the lasing elements.